Letoff foe looms



A. PALMER ETAL LETOFF FOR LUQMS 2 Sheets-Sheet 1 I Filed May 10, 1945 Oct. 5, 1948.

LE'I'OFF FOR LOOMS 2 Sheets-Sheet 2 Filed May 10, 1945 Patented Oct. 5, 1948 UNITED STATES oFFlcE LETOFF FOR LOOMS Massachusetts Application May 10, 1945, Serial No. S92E86 '26 Claims. 1

This invention relates to improvements in loom letofis and it is the general object of the invention to provide means controlled by the warp ten sion for turning the Warp beam.

There is a tendency in the textile industry to utilize warp beams of ever increasing diameter for the purpose of holding larger supplies of warp. As the diameter of these beams increase their weight interferes with proper letting on of the warp when conventional types of lctoff mechanisms are employed. Ordinarily the force for moving the warp beam is transmitted through the warp threads, but as the inertia of the beam increases an amount of force required for turning the beam is more than can properly be trans= mitted through the warp. It is an important object of the present invention to provide means for applying a continuous rotary force to the beam control in such a way that the rate of application of the force can be altered to meet the conditions of the warp.

It is another object of the invention to provide a constantly running motor driven unit connected to the warp beam and subject to speed variations controlled by indications derived from the warp tension in such a way that when the tension is low the unit will operate at a slow speed, but when the tension is high the unit will operate faster to pay off warp from the beam.

It is a still further object of the invention to control the speed of the motor forming part of the aforesaid unit by means of an electronic circuit wherein fluctuations in the control grid potential are derived from variations in warp tension.

With these and other objects in view which will appear as the description proceeds, our in vention resides in the combination and arrange- Fig. 3 is an enlarged vertica1 detailed section on line 3-3 of Fig. 2.

Fig. 4 is a section on line 4-4 of Fig. 3.

Fig. 5 is a view looking in the direction of arrow 5, Fig. 1, showing the electronic circuit controlling gauge which is responsive to variations in warp tension, a

Fig. 6 is a vertical section on line 6-6 of Fig.

Fig. 7 is a vertical section through the driving gear of the reduction unit showing the type of friction drive which may conveniently be used with the invention, and. I

Fig. 8 is a diagrammatic view showing the electric circuits employed for controlling the motor.

Referring to Figs. 1 and 2, there is shown a loom frame Iii to which are attached'upper and lower rearwardly extending stands I l and I2, respectively. A whip roll I3 is mounted on the upper end of an arm it pivoted as at I5 to the stand II. A spring to may be employed to hold the arm normally and rearwardly or to the left as viewed in Fig. 1. A stop I! on the bottom of arm is engages a shoulder IE on the stand H to limit rearward movement of arm l4 and the whip roll. Forward movementv of the whip roll is limited by an adjusting screw l9 mounted on stand I l for engagement with the front part of arm- I4. The warp W derived from the beam B passes over the whip roll and then forwardly to harness'frames and other weaving instrumentalities not shown. The whip roll I3 is capable of a limited back and forth motion determined by the stops l8 and IE but tends normally to be in the rear position shown in Fig. 1. At the time of beatup or when the harnesses are wide open forward tension in the warp may move the whip roll to the right as viewed in Fig. 1.

The stand I2 is provided with a bearing through-which extends a gudgeon 26 projecting laterally from the-head 27 of the warp beam. The gudgeon is mounted for free rotation in its hearing and is the means for supporting the adjacent end of the beam. It will be. understood that suitable supports are provided for the opposite end of the warp beam and whip roll and that during the loom operation consumption of the warp requires must be applied to it to turn it on its bearings.

The matter thus far described except as noted hereinafter forms no part of the present invention and may be made as usual.

In carrying the invention into eflect there are provided a gear reducer unit R, a motor unit M, a control unit C responsive to variations in warp tension, and the electric circuits shown in Fig. 8.

The gudgeon 26 has secured thereto a gear 30 meshing with a second gear 3| mounted on a low turning shaft 32 of the gear reducerR. As shown in Fig. 7 the gear 3| has a web 34 held friction- I ally between plates or disks 35 and'36. The plate 35 has a hub 31 secured to shaft 32 and the plates are held in frictional engagement with the web by bolts a. Ordinarily the plates are so set as to transmit an operating force from shaft 32 to gear SI for the p rpose of turning the gear 30, but if for any reason the shaft I: should be held against rotation the gear II can slip with respect to it. The unit R is mounted on a support 40 located on the fioor atone side of the warp beam but held in fixed position with respect to the loom frame as at ll. A small bracket 42 extending upwardly from the support 40 has moimted thereon a fractional horse power motor I! the shaft ll of which is connected by coupling H to the fast turning input shaft ll of the reducer unit R.

The mechanism in the reducer is not set forth in detail herein but operates in such a manner that when shaft 4! is turned by operation of the motor 43 the output shaft 82 will turn at a slowrate. The mechanism within the reducer includes a worm gear 41 and a worm ll meshing therewithanditisbecause oithewormthatthetype ofdriveforgear 3i showninl'igfl'lisused.

The control unit is mounted on the whip roll or at least held in such a position that it can rei spend to variations in warp tension without moving forwardly with the warp. As shown herein a shell I! having end plates 58 houses ball bearings U which engage the whip roll it. By means of the ball bearings the whip roll can turn with respect to the shell II, although this is not an essential feature inasmuch as rotation of the whip roll with respect to its supporting arm it may be prevented if desired as by a set screw it. A couna small unidirectional pulsating current flows from secondary winding ll over wire I! to plate P of tube 82 and across to the cathode It and thence by wires II and III, unit I" and wire it to the armature or the motor and back by the center tap 88 to the winding II. In a similar manner the .winding ll establishes a circuit through the tube It andvthe motor armature.

. The two tubes act to rectify the alternating eurterweight 59 secured to shell II keeps the unit C in balance so that the pressure reading will be accurate.

The shell H has extending downwardly therefrom an arm 80 on which is mounted a gauge or warptension meter T. This gauge has a foot ii secured as at 2 to the arm ll. Parallel spaced fingers 83 extend from the base 'i and are adapted to have a small section of warp pasmbetween them as suggested in Figs. 5 and 8. An upright 85 suppo the gauge and aifords support as at I! for a small shaft 88 mounted for'ro'tation on the upright and having secured thereto a small pinion 81. This pinion meshes with a rack rod 8 guided as indicated in Fig. 8 with respect to the upright 65 and having the lower end thereof provided with a pressure detecting foot II which normally engages the warp threads extending between the iingers 63. The tension meter T'of itself forms no part of the invention except as it closes a contactas will be described. Reference may be had to patent to Payne No. 1,817,203 after which the meter T is patterned.

The end of shaft 88 opposite the pinion has secured thereto and insulated therefrom a contact sweep arm H which rotates with shaft II and is adapted for engagement with an electric contact 12 clamped as at 13 to the insulated rim 1 held as at It on the upright Ii. A light spring 11 guided in upright 65 tends to lower the detecting foot 10 but this tendency is resisted by the tension of the warp W in engagement with the detector foot. The contact 12 can be set at any desired angular position around the disk 14 so that engagement between the arm II and the contact I! may be effected for any selected vertical position of the detector foot 10 with respect to the controller 0.

Fig. 8 shows diagrammatically a form of circuit which has been used with the invention disclosed herein. The transformer T has its secondary divided into two windings 8. and ii each capable of giving current at a sufiiciently high voltage to operate the armature 18 of the motor 43. Two electronic tubes 82 and it are employed and a rent so that a unidirectional current can fiow through the tubes to the armature causing the latter to turn normally at a slow rate. The conditions which permit this flow of current will now be described.

A second transformer T has secondary windings I" and Ill connected to acenter tap m. Since the tubes 82 and I! are gas filled it is desirable that they be protected against excess current and for this purpose resistances R and R. are used.

Bridged across the direct current wires II and I! is a variable resistance R: which serves as a control for the initial or normal speed of the motor. Resistances R3 and R4 are relatively high, resistance RA in one instance in which the invention has been used bein about one quarter megohm and resistance R3 being about one half of resistance RI. The lower right hand part of Fig. 8 represents diagrammatically the swinging contact arm H and the adjustable but normally stationary contact 12 shown in more detail in Piss. 5 and 6.

The primary I05 of transformer T is suwlied with power by wires I" and III which are connected to the same source as are wires Ill and I connected to the primary of transformer T. AresistanceRiisconnectedinwire iliinseries with the primary Ill and cooperates with the inductance of primary I" to create a 90' phase displacement of the secondaries I" and III with respect to the power lines III and I" and also transformer T the secondaries of which are connected to plates P and P ofthe tubes 82 and II. Thenormalbiasof gridGis'determinedby the following circuit: secondary i, resistance R, gridG, cathode ll, wires ll, ill and Iii, slidingcontact i|2forresistancem.theupperpart of resistance R2, wire ll, resistance R8. wire Ill, and center tap it! backto the secondary ill. Inthiscircuit the upperpartof resistance Rlimposesadirectcurrentcomponentonthe secondary alternating current component derived from winding ill, and this direct current component is reckoned from a potential level below the zero potential level of the line alternating current supplied by wires I and Ill. The combination of the direct and secondary alternating components provides a resultant alternating current. when the positive secondaryalternationisaddedtothedirectcurrent it provides a positive wave for the resultant current the maximum potential of which will ordi- .narily be above the aero potential of the line current level. The zero level or axis of the resultant wave is therefore below the zero level or axis of the line alternating current, but this.

resultant wave axis can be raised and lowered relatively to the line alternating current axis by changing the location of sliding contact 2.

The amount of current which can flow through grid G for the normal operation of the motor will be dependent upon the extent to which the positive resultant wave rises above the axis of the line alternating current. Contact II2 will ordinarily be set so that this positive resultant wave will be above the line alternating current zero of the plate P sufficiently to provide the current needed to drive the motor at its normal speed, but current flowing through tube 82 can be increased by raising the axis of the resultant wave so that more of the positive part of the resultant wave will be above the axis of the line alternating current at the plate. The raising of the resultantwave axis is effected by closure of the contacts II and 12, as will be described.

That part of resistance R2between wire 85 and sliding contact I i2 determines the average potential of grid G. Sliding contact H2 can be set to give grid G any desired potential to permit a smooth variation in current passing through tube 8'2 from zero to maximum. Under normal conditions contact II2 will be set so that the potential of grid G will allow enough current to how through armature I8 to allow the motor to run at a constant speed which is somewhat less than that required to turn the warp beam fast enough to supply warp as the latter is consumed. The contacts 'II and 12 are of course out of engagement with each other under these normal conditions.

As weaving continues tension in the warp will increase due to consumption of the warp and swinging arm Ii will ultimately engage contact 12 and establish the followinggrid circuit: secondary Hi8, protective resistance R, grid G, cathode 42, wires 90, H and III, sliding contact H2, lower part of resistance R2, wire 86, resistance R4, wire IIB, contacts 12 and II, wires H and U2 to center tap I82 and back to secondary "I. In this last circuit it will be noted that resistance R3 is bypassed and the resistance R4 is substituted for it. The effect of substituting the lower part of resistance R2 and resistance R4 for resistance R8 and the upper part of resistances R2 is to raise the aforesaid axis of the resultant wave, thereby raising the positive part of the resultant wave to higher level relatively to the line alternating current or plate axis than existed previously. More current therefore flows through the tube 82 to the armature I8 and motor speed is increased. The motor will run at its increased speed until it has caused the warp beam to unwind enough warp to offset the previously increased warp tension, whereupon arm II will move away from contact 12 and the normal grid bias circuit will be reestablished.

Similar conditions exist for grid G of tube 83 and during closure of contacts II and 12 the two tubes act to supply a unidirectional current at a value above the normal current for operation of the motor. v

Fig. 8 shows a condenser K between wire H0 and center tap I82. Warp tension temporarily increases at beat-up and again when the harnesses are wide open. When the loom is running at high speeds, therefore, there will be several temporary or periodic increases in warp tension each second. The effect of the condenser is'to smooth out the impulses which may result from closure of contacts II and 12 due to these periodic tension increases. As a result, the grids respond to the integrating effect which the condenser has on these periodic impulses rather than to each individual impulse, and the motor has a smoother operation. Without the condenser the motor response would be instantaneous, which might shorten the life of the motor. The period during which the aforesaid integration of impulses occurs .may be varied by changing the size of condenser K. The rate at which the condenser is charged is determined by resistances RI and R4 and the rectified grid current as determined by the upper part of resist. ance R2. The condenser ischarged through resistance R4 and discharges at a slower rate through resistance R3.

If for any reason warp should become too slack, necessitating reversal of motor 43, reversing switch I20 can be thrown to reverse the field. Another feature of the invention relates to provision for stopping the motor 43 whenever the loom is stopped. It will be apparent that if the motor 43 should continue to run after the loom had been stopped due to warp or filling fault, the warp could continue to unwind and create a condition which would require attention from the weaver when the .loom was restarted. In order to take care of this condition we establish a control between the motor circuit and some part of the loom, such as the shipper handle, which changes its position when the loom is stopped.

Referring particularly to Fig. 8, there i shown a shipper handle I25 which may be pivoted as at I28 and have a depending arm I21 for engagement with the switch blade I28 of a switch unit when the shipper handle is in running position it will cause blade I28 to engage the electrode I3I and thereby connect the armature 18 to the oathodes 82 and 93. When the shipper handle moves to stopping position, however, the blade I28 moves away from the electrode I3I and interrupts the armature circuit, whereupon the motor stops.

From the foregoing it will be seen that we have provided a loom letofl employing a motor which runs continuously and normally at a rate too slow to supply suillcient warp for the weaving operation, together with means to increase the speed of the motor above its normal minimum rate to turn the warp beam sufficiently to maintain uniform tension. It will also be seen that the control for the motor is an electronic circuit which responds to diminution in warp tension without regard to the position of the whip roll. Furthermore, it will be seen that the position of the sliding contact H2 determines the normal minimum currentwhich flows through the armature and that a variation in armature speed can be obtained throughout a wide range for normal operation due to the fact that the grids of the tubes are out of phase with their corresponding tube plates by It will also be noted that when the contact is closed at the controller-C the potential of the grid is altered due to a 7 change in the axis of the resultant wave relativeiy to the line or plate alternating current which results when resistance R4 is substituted for resistance R3 in the grid potential circuit. In this connection it will also be seen that the resistance R2 has two parts, one above contact H! which contributes ,to the determination oi the grid potential under normal motor speed conditions and the other part or which is below contact H2 and contributes to the increase in motor speed when the contact is closed at the controller 0. Also, the condenser K has the eiiect of integrating and smoothing out impulses derived from the controller C when periodic increases or warp tensionoccur due to beat-up and harness opening. The condenser K affects the potential of the grids in such a way as to give smoother control for the armature current than would be possible if the condenser were omitted. It will also be seen that the switch unit I" interrupts the circuit to the armature whenever the shipper handle is in stopping position, thereby preventing running of the motor whenever the loom is stopped.

Having thus described our invention it will be seen that changes and modifications may be made therein by those skilled in the art' without departing from the spirit and scope or the invention and we do not wish to be limited to the details herein disclosed, but what we claim is:

1. In a letoii mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running, electric means causing the motor to run continuously during loom operation but normally at a rate insuillcient to enable the beam to supply the warp needed for the weaving operation, and means responsive to increased tension in the warp causing the motor to run faster than the normal speed thereof to enable the beam to supply the warp needed for the weaving operation.

2. In a letofl mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp 'when the motor is running, electric circuit means capable of causing the motor to turn at varying rates of speed and normally causing the motor to turn at a rate too slow to enable the beam to supply the warp needed for the weaving operation when the warp tension is below a given point, and a controller for said electric circuit means operative when the warp tension reaches said given point to increase the speed 01 the motor to enable the beam to supply warp at a faster rate.

3. In a letofi mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running, electric means capable of driving the motor at different speeds and normally operative to drive the motor at a speed insufiicient to enable the beam to supply warp at the rate needed for the weaving operation, and a controller for said electric means responsive to changes in warp tension and causing the electric means ,to increase the speed or the motor when 8 thewarptensionincreaeestoagivenpoint. therebyincreasetherateatwhiehthebeam plies warp.

4. In a letoiimechanism iora ioomhavint. warp beam supplying warp the'tension which increases when the beam turns at a given rate insuiiicient to supply the amount or. warp needed for the weaving operation. anelectri motor operatively connected to the beam to on turning of the latter when the motor is running. electric circuit means including the motor and normally operative to cause the motor tosturn the beam at said given rate. tension means-responsive to increases in tension in the warp'and having a contact whichis closed when a given degree or tension occurs in thewarp. and electric controller means including said contact and connected to said electric circuit means .and effective to cause the latter to turn the motor at an increased speed when said contact is closed.

5. In a letoii mechanism for a loom having a war beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, an electric motor operatively eonnectedtothebeamtocauseturningotthelatter when-the motor is running. electric circuit means normally causing the motor to turn at a given minimum rate too slow to cause the beam to supply suiiicient warp tor the weaving operation, tension means connected directly to the warp and eiiective to close an electric contact when the warp tension increases to a given point. and electric control means including said contact and electrically connected to said electric circult means causing the latter to turn the motor at a rate above said given minimum rate when said contact is closed.

6. In a letoi! mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to suppl the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running. an electronic tube including a grid, electric circuit means including the tube and motor, primary electric controller means for the grid operative under normal conditions to maintain the grid in such electric condition a to permit an amount of current to flow in said electric circuit means suilicient-only to cause the motor to turn the warp beam at too slow a rate to supply the warp required for weaving, an indicator responsive to warp tension'and closing a contact when the warp tension increases to a given point, and secondary electric controller means including the contact and grid and operative when the contact is closed to alter the electric condition of the grid so that more current flows through said tube with resultant increase in the rate of turning of the motor.

7. In a letoii' mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running, an electronic tube including a grid, electric circuit mean including the tube and motor tending normally to cause enough current to flow through the tube and motor to 9 I such electric condition as to permit only that amount of current to flow through the tube which will cause turning of the motor at a rate too slow to enable the beam to supply the warp required tor weaving, a tension indicator which closes an electric contact when the warp tension increases to a given point, and additional electric controller means connected to the grid and operative upon closure 01' said contact to change the electric condition of the grid in such-manner that the grid permits more current to flow through the tube and motor to increase the speed of the latter.

8. In a letoff mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running, an electronic tube including, a grid, electric circuit means including a grid and motor tending normally to turn the motor at a speed sufflciently high to cause the beam to supply the warp required in the weaving operation, electric control means for the grid normally maintaining an electric condition on the grid by which the latter permits only enough electric current to flow through the tube and motor to operate the latter at a relatively low speed insufficient to enable the beam to supply the warp needed for the weaving operation, and additional electric control means for the grid responsive to changes in warp tension and operative upon increase of tension in the warp to a given point to change the electric condition 01 the grid so that an increased amount of current passes through the tube and motor to increase the speed of the latter.

9. In a letofi mechanism for a loom having a beam which turns to supply warp the tension of which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a motor operatively connected to the beam to cause turning of the beam to supply warp when the motor is running, means normally operative when'the warp tension is below a given degree causing the motor to turn the beam at a rate insuillcient to supply the warp needed for the weaving operation, and other means under control of the warp and operative when the warp tension increases to said given degree to cause the motor to run faster and turn the beam at an increased rate.

10. In a letofi' mechanism for a loom having a war beam which turns to supply warp the tension of which increases when the beam turns at too slow a rate to supply the warp needed for the weaving operation, an electric motor having an armature the rate of rotation of which increases as the current flowing therethrough increases, driving connections between the armature and the beam causing the latter to turn when the armature turns, an electronic tube having a grid, a source of electric current, electric circuit means including said source, tube and armature and tending normally to turn the armature at a relatively high rate of speed sufficient to enable the beam to supply the warp needed for weaving, a primary control for the grid normally operative to maintain the latter at such electric condition as will enable only enough current to flow through said circuit means to turn the armature at a relatively low rate too slow to enable the beam to supply the warp'required for the weaving operation, and a secondary controller 10 for said grid operative when the warp tension increases to a given point to alter the electric condition of the grid so that the latter permits a larger current to flow through said electric circuit means to turn said motor at said relatively high speed.

11. In a letoif mechanism for a loom having a warp beam which rotates to supply warp the tension or which increases when the beam turns too slowly to supply the warp needed for the weaving operation, a direct current motor having a field coil and an armature, driving connections between the armature and the beam causing the latter to turn when the armature turns, a source of direct current connected to the field coil, a

source ofalternating current, an electronic tube having a grid, electric "circuit means including said source of alternating current, motor and tube, the latter permitting current to flow therethrough in only one direction so that unidirectional current flows through the armature, an electric resistance connected across said source of direct current, control means for the grid including a part of said resistance and normally effective to maintain said grid at such electric condition that said grid permits only an amount of current to pass through the tube and armature which will turn the latter at a rate too slow to enable the beam to supply the warp required for the weaving operation, and other control means for the grid including another part of said resistance and rendered operative upon increase of tension of the warp to a given point to alter the electric condition of the grid in such manner that the grid enables increased unidirectional current to flow from said source of alternating current through the armature to increase the speed of the latter suihciently" to enable the beam to supply the warp needed for the weaving operation.

In a letofi mechanism for a loom having a warp beam which turns to supplywarp the tension of which increases when the beam turns too slowly to supply the warp needed for the a weaving, a grid forming part of said tube, a resistance connected across said source of direct current, two other resistances, grid control circuit means including said source of alternating current, one of said other resistances, a part 01' said one resistance, and the grid normally operative to maintain the latter at such electric condition as will enable only enough current to flow from said alternating current source through said tube to the armature to turn the latter at a relatively low rate too slow to enable the beam to supply warp at the rate needed for the weaving operation, and other control circuit means for the grid including said other resistance and the other part of said one resistance, said source of alternating current and grid operative upon increase of warp tension to a given point to alter the electric condition of the grid so that the latter enables said circuit means to cause increased current to and an armature operatively connected to the beam to turn the latter when the armature turns,

a source of direct current for the field coil, 9.

source of alternating current, an-e1ectronic tube permitting current to pass therethrough in one direction only, electric circuit means including the source of alternating current, tube and armature tending normally to operate the latter at a relatively high speed suflicient to enable the beam to supply the warp needed for weaving, a grid forming part of the tube, a primary circuit for the grid including said source of alternating current, means in said primary circuit to superimpose'a part of the voltage of said source of direct current upon the current from said source of alternating current to create such an electric condition on the grid as will permit the latter to enable only enough current to fiow through said tube to turn the armature at a relatively slow rate insumcient to enable the beam to supply the warp required for the weaving operation when the warp tension.

is below a given point, and a secondary control circuit for the grid operative when the warp tension increases to a given point to change the amount of direct current voltage derived from the source of direct current and imposed upon the voltage derived from the source of alternating current to alter the electric condition of the grid in such manner that the grid enables an increased amountof current to ilow from said source of alternating current through the armature for the purpose of increasing the speed of the latter.

14. In a letofi mechanism for a loom having a rotatable beam supplying warp the tension oi which increases when the beam turns too slowly to supply suiiicient warp for the weaving operation, an electric motor operatively connected 'to the beam to cause turning of the latter when the motor runs, an electric contact closed when warp tension increases to a given point, an electronic tube, a source of electric power, motor circuit means including the tube, source and motor tending normally to cause the motor to run at a high enough rate to turn the beam fast enough to supply suflicient warp for the weaving operation, a grid forming part of the tube, electric resistance means, grid circuit means including said source and a part of said resistance means normally maintaining the grid at such electric condition as to enable current to flow into said motor circuit means to cause continuous operation of the motor at a rate too slow to enable the beam to supply the warp needed for the weaving operation, a second grid circuit means including said grid, source, the other part or said resistance means, and said contact, said second grid circuit being closed when said contact is closed and eflective to alter the electric condition of the grid so that the latter permits increased current to flow through the tube and said motor circuit means to increase the speed of the motor, and a condenser connected in parallel with said contact and .said other part of the resistance means.

15. In letofl mechanism for a loom having a beam which rotates to supply warp the tension oi which increases when the beam turns too slowly to supply warp needed for the weaving operation. 76

12 i an electric motor operatively connected to the beam to turn the latter when the motor runs, a source or electric power, an electronic tube including a grid, motor circuit means including said source, tube and motor tending normally to cause the motor to turn fast enough to enable the beam to supply the warp needed for the weaving operation, an electric contact closed whenever the warp tension increases to a given point, grid circuit means normally maintaining the grid at such electric condition as will permit current to flow through said motor circuit means to cause continuous operation of the motor at a rate too slow to enable the beam to supply the warp needed for the weaving operation, connections between said electric contact and said grid circuit means producing an eifect which alters the electric condition of the grid whenever said contact. is closed to enable more current to flow through the tube and said motor circuit means to increase the speed of the motor, and condenser means in parallel with said contact and connected to said grid circuit means and causing an averaging of several successive eflects caused by closure of said contact to prevent sudden changes in said grid circuit upon closure of said contact.

16. In a letci! mechanism for a loom having a part which is in one position when the loom is operating and is in another position when the loom is stopped, a warp beam which turns to supply warp for the weaving operation, an electric motor operatively connected to the beam and causing the latter to turn when the motor runs, a switch under control of said part, and electric means including the motor and switch operative to cause continuous running or the motor to cause turning of the beam whenever the loom is operating and said part is in said one position and closes said switch, said electric means being incapable of causing the motor to run when the loom is stopped and said switch is open due to the fact that said part is in said other position.

17. In a letoii mechanism for a loom having a beam which turns to deliver warp for theweaving process, an electric motor operatively con nected to the beam to cause turning thereof to deliver warp when the motor is running, elec-'- tronic tube means including control grid means, electric circuit means including the tube means and motor normally tending to cause an electric change in the motor to efiect delivery oi warp by the beam at a given rate, and grid control means responsive to changes in warp tension normally enabling the grid means to prevent the electric circuit means from causing said change in the motor to eilect delivery of warp at said rate, said grid control means eflective when the warp attains a given tension to alter the grid means in such manner as to permit said electric circuit means to effect said change in the motor to cause delivery of warp at said rate.

18. In a letoi! mechanism for a loom having a beam which turns to deliver warp tor the weaving process, an electric motor operatively connected to the beam to cause turning thereof to deliver warp when the motor is running, electric circuit means including an electronic tube tending'to rim the motor at a rate sutlicient to relieve excess warp tension and to deliver the warp needed for the weaving process, a grid in said tube controlling said electric circuit means, and grid circuit means causing the grid to prevent the electric circuit means from running the motor at said rate when the warp tension is less than said excess tension but causing the grid to enable the electric circuit means to run the motor at said rate when the warp attains said excess tension.

19. In a letoff mechanism for a loom having a beam which turns to deliver warp for the weaving process, an electric motor operatively connected to the beam to cause turning thereof during loom operation to deliver warp when the motor is running, electric circuit means including an electronic tube normally tending to run the motor at a rate sufficient to relieve excess warp tension and to deliver the warp needed for the,

weaving process, a grid in said tube controlling said electric circuit means, grid circuit means causing the grid to prevent the electric circuit means from running the motor at said rate when the warp tension is less than said excess tension but causing the grid to enable the electric circuit means to run the motor at said rate when the warp attains said excess tension, and means to prevent said electric circuit means from causing said motor to run when loom operation is stopped.

20. In letoii mechanism for a loom having a warp beam operatively connected to an electric motor which when running turns the beam to deliver warp for the weaving operation, a contact capable of assuming two conditions in one of which the contact is open and in the other of which the contact is closed, said contact being under control of the warp and being in one condition thereof when the tension of the warp is less than a given maximum and being in the other condition thereof when the warp attains said given maximum, motor operating electric circuit means including electronic tube means normally tending to cause the motor to run at a rate sufficient to relieve said maximum tension, controlling grid means for the tube means, and grid circuit means controlled by said contact and effective when thelatter is in said one condition thereof to enable the grid means to prevent said motor operating electric circuit means from causing the motor to run at said rate and effective when said contact is in the other condition thereof to alter said grid means to enable said motor operating electric circuit means to cause the motor to run at said rate.

21. In letofl mechanism for a loon. having a warp beam delivering warp which attains a given maximum tension during loom operation, an electric motor which when running turns the beam to deliver warp, said motor being of the shunt wound type and having an excited field and an armature, armature controlling electric circuit means including an electronic tube normally tending to turn the motor at a rate sufficient to r reduce said maximum warp tension, a control grid in said electronic tube, and grid circuit means controlled by the warp tension and effectiv when said tension is less than said maximum to enable the grid to prevent the armature circuit means from causing said motor to run at said rate, said grid circuit means being effective when the warp attains said maximum tension to alter the elecis constantly energized during loom operation and having an armature independent of the field,

g 14 a transformer having a secondary provided with a center tap and constituting a source of alternating current, a pair of electronic gas containing tubes having plates one of which is connected to one end of said secondary and the other of which is connected to the other end of said secondary, electric circuit means including said tubes, secondary and armature and connected to said center tap and normally tending to cause the motor to run at a rate suflicient to reduce said maximum warp tension, a control grid for each tube, and grid controlling circuit means under control of the warp tension and effective when the warp tension is less than said maximum to enable the grids to prevent said electric circuit means from running the motor at said rate, said grid controlling circuit means being effective when the warp attains said maximum tension to alter the electric condition of said grids to enable said electric circuit means to cause said motor to run at said rate. 23. In a letoff mechanism for a loom having a beam which turns to deliver warp for the weaving process, an electric motor operatively connected to the beam to cause turning thereof to deliver warp when the motor is running, electronic tube means including control grid means, a source of alternating current, electric circuit means including said source, the tube means and motor normally tending to cause an electric change in the motor to effect delivery of warp by the beam at a given rate, a second source delivering alternating current out of phase with the alternating current of the first named source,

mally enabling the grid means to prevent the electric circuit means from causing said change in the motor to effect delivery of warp at said rate, said grid controlling means effective when the warp attains a given tension to alter the grid means in such manner as to permit said electric circuit means to effect said change, in the motor to cause delivery of warp at said rate.

24. In letoif mechanism for a loom having a beam which turns 'to deliver warp for the weaving process, an electric motor operatively connected to the beam to cause turning thereof to deliver warp when the motor is running, electric circuit means including an electronic tube tending to run the motor at a rate suflicient to relieve excess warp tension and to deliver the warp needed for the weaving process, a grid in said tube controlling said electric circuit means, grid circuit means causing the grid to prevent the electric circuit means from running the motor at said ratewhen the warp tension is less than said excess tension but causing the grid to enablethe'elec'tric circuit means to run the motor at said rate when the warp attains said excess tension, and electric means to reverse the direction of turning of the motor.

25. In a letoif mechanism for a loom having motor at a rate sufficient to relieve excess warp tension and to deliver the warp needed for the weaving process, a grid in said tube controllin said electric circuit means, grid circuit means causing the grid to prevent the electric circuit means from running the motor at said rate when the warp tension is less than said excess tension 15 but causing the grid to enable the electric circuit means to run the motor at said rate when the -warp attains said excess tension, and electric switch means to reverse the held of the motor.

26. In letofl mechanism for a loom-having a warp beam delivering warp which attains a given maximum tension during loom operation, a shunt wound type electric motor having a held and an armature effective when the loom is running normally to turn the beam to deliver warp, electric means to reverse the held to cause reverse running of the motor, armature controlling electric circuit means including an electronic tube normally tending to turn the motor at a rate sumcient to reduce said maximum warp tension, 9. 15

control grid in said electronic tube, and grid circuit means controlled by the warp tension and effective when said tension is less than said maximum to enable the grid to prevent the armature circuit means from causing said motor to run 20 at said rate, said grid circuit means'being effective when the warp attains said maximum tension to alter the electric condition oi 'the grid in such manner as to enable said armature circuit means to energize the armature in such manner as to cause the motor to run at said rate.

ALBERT PALMER. VICTOR F. SEPAVICl-I.

REFERENCES CITED The following references are of record in the flle of this patent: 

